It must be noted that Elektron manufactures the hardware that uses these OLED components, not the OLEDs themselves.
The manufacturer of this particular OLED is probably some no-name brand, but the “brand name” version wouldn’t have been any better. There are no “premium”-level manufacturers of this type of component in this form-factor/resolution/etc.
Yes, each LED in the OLED consumes current, so the more that are on, the more power it will draw. This certainly could account for some slight dimness in certain pixels/rows.
There can be tolerances in say, the voltage regulators or caps or even the OLED itself, but I doubt you’re going to get a much better “specimen.”